A charging method includes the following operations: charging an auxiliary power source and at least one charging power source simultaneously, in which a power demand of the auxiliary power source is a first consideration, and a power demand of the at least one charging power source is a second consideration; detecting an auxiliary current value of the auxiliary power source and a total charging current value of the at least one charging power source; and stopping charging the auxiliary power source when a sum of the auxiliary current value and the total charging current value is greater than a current threshold value.